The British High Commission and Nigerian authorities negotiated the release of the three hostages who survived and the kidnapping is being investigated, a spokesperson for the British Foreign Office, whose name was not given, was quoted as saying.
It is understood that Mr Squire and fellow Christian charity workers David and Shirley Donovan and Alanna Carson were working as missionaries when they were abducted from their accommodation in the early hours of 13 October.
Small houses are seen by the bank of a river in Delta State, Nigeria.
The British government says one United Kingdom missionary who was kidnapped in Nigeria last month has been killed but three others have been freed. The Foreign Office said it could not comment during an ongoing investigation.
Ian Squire was killed following the kidnap on October 14.
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Relatives of the four said they were "delighted and relieved" that Ms Carson, and Dr and Mrs Donovan, had returned safely.
"Our thoughts are now with the family and friends of Ian as we come to terms with his sad death", they said in a statement issued on their behalf.
"This has been a traumatic time for our loved ones who were kidnapped and for their families and friends here in the United Kingdom", it said.
The FCO now advises against all but essential travel to much of Delta state, saying there is a "high threat of criminal kidnap".
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